The invention relates to the non-invasive ultrasonic diagnosis of lesions on tooth surfaces or under dental restorations such as gold crowns and other dental restorations. The invention further relates to the non-invasive ultrasonic diagnosis of lesions on interproximal tooth surfaces and/or interproximal areas of dental restorations such as gold crowns and other dental restorations. The invention also relates to the non-invasive ultrasonic diagnosis of periodontal disease. Tooth lesions diagnosed could be enamel caries, dentinal caries and cracks in the tooth. Similarly, periodontal disease diagnosed could be gingivitis and periodontitis. In particular, the invention relates to ultrasonic stress waves imparted through the tooth (transmitted from one transducer through the tooth, and/or gum and bone to a second receiving transducer) or through a dental restoration for the detection of said lesions.
Non-destructive material evaluation is the identification of physical and mechanical properties of a piece of material without altering its end-use capabilities. One effective technique used to provide accurate information pertaining to the material properties is ultrasonic Stress Wave Timing. Stress waves, for the purpose of this patent, are the propagation of stresses distributed longitudinally through material. Wavelength can encompass any range. The preferred embodiment is between ten and thirty megahertz. As indicated, stress wave can be an ultrasonic wave pulse. The basic principle of stress wave timing is to use a stress wave to measure the speed of sound transmission by recording the time it takes to pass through material and/or attenuation of induced stress wave. The speed with which sound waves travel through a material is dependent upon the materials properties. The transmission of sound through materials and the related rates of travel and attenuations is a well-understood art. All of the above cited U.S. patents, other than one (U.S. Pat. No. 5,570,182), have used a related but different method of evaluating materials with ultrasound. They have looked at the ultrasound Pulse-Echo that is returned from structures or boundaries in the tooth being evaluated, that is they use an ultrasonic transducer to transmitted a ultrasound pulse into the tooth and then used the same transducer, or another very close to it, to receive the reflected energy, the echo of that pulse, off internal layers or other structures within the tooth they are looking into. U.S. Pat. Nos. 5,874,677, 6,162,177 and 6,190,318 transmit surface (Rayleigh) waves and these patents only look for the pulse-echo from this surface wave. They do not look through the tooth; they look around the outer surface of the tooth, to diagnose carious lesions. U.S. Pat. No. 5,570,182 uses light instead of sound as a medium to evaluate materials. Many articles have been published on the use of Pulse-Echo ultrasound in teeth also. (Ultrasonic Pulse-Echo Measurements in Teeth. FE. Barber, S. Lees, R. R. Lobene. Archs oral Biol., Vol. 14, 745-760, 1969), (Observation of Internal Structures of Teeth by Ultrasonography. G. Baum, I. Greenwood, S. Slawski, R. Smirnow. Science, Vol. 139, 495-496, 1962.
According to prior art, sound in dental materials travels at different speeds according to the material it is passing through. The slowest is the tooth""s pulp section, which has sound transmission characteristics very similar to water (Examination of the Contents of the Pulp Cavity in Teeth. G. Kossoff, C. J. Sharpe. Ultrasonic, 77-83, 1966), next is dentine at approximately four times faster. The fastest is in enamel at about six times faster than water (Determination of Ultrasonic Velocity in Human Enamel and Dentine. S. Y Ng, P. A. Payne, N. A. Cartledge, M. W. J. Ferguson. Archs oral Biol., Vol. 34, No. 5, 341-345, 1988). Dental caries, in general, would have a different transmission time, the time it takes for the stress (acoustic) wave to travel from the transmitting transducer to the receiving transducer, so the location and severity of material change (caries) can be found easily and quickly by recording multiple transmission times over an area. By using oscilloscopes, or other measuring or recording devices, transmission time, wave attenuation, transit times and wave shape, thus time and speed, can be recorded and evaluated. The sequence of transit times can be mapped onto the path taken by the receive and transmit transducer pairs as they are mechanically or electronically translated about the tooth. The resulting map can be thought of as an image of the shortest times taken by the stress wave through that region of the tooth defined by the transducer locations. Regions of anomalous transit times are interpreted as regions of dental caries or some other defect in the tooth structure. Mapping is the preferred embodiment of imaging, of the material (tooth and gums) that can be used to diagnose lesions such as enamel caries, dentinal caries and cracks in the tooth. (Development and Application of an Ultrasonic Imaging System for Dental Diagnosis. H. Fukukita, T. Yanco, A. Fukumoto, K. Sawada, T. Fujimasa, and I. Sciaenidae. Journal Of Clinical Ultrasound No. 13, 597-600, October 1985).
In particular, the invention relates to ultrasonic stress waves imparted through the tooth or dental restoration for the detection of these lesions. Periodontal disease, such as gingivitis, periodontitis can be diagnosed also.
Dental caries (dental cavities or tooth decay) is a disease manifested by local demineralization of the enamel and dentine of the tooth caused by dental plaque. The demineralization process progresses from the outer enamel surface of the tooth through the entire thickness of the enamel and into the dentine. Caries lesions of occlusal (biting surface), buccal (cheek side) and lingual (tongue side) surfaces can be diagnosed by mechanical probing and/or visual inspection. It is difficult or impossible to find small and medium size lesions of interproximal surfaces hidden by the gums and/or adjacent teeth. These can usually only be found with dental X-rays (radiographs). Although the use of bitewing radiographs is often used as a tool in the diagnosis of proximal caries lesions, this method has several weaknesses because of its relative insensitivity and user dependence in terms of technical skill and interpretation (Waggoner W., F. Crall J. J. Quintessence International 11/1984: 1163-1173). It should be noted that bitewing radiographs have a high proportion of X-rays taken in the dental office. This is contrary to current trends in safety standards that support every effort aimed at reducing the exposure to ionizing irradiation.
Caries lesions not adjacent to a dental restoration on a tooth surface site are known as primary caries, while caries lesions in contact with a dental restoration at the tooth surface are known as secondary caries. Secondary caries would be caries next to a filling or under a gold crown.
In conventional methods X-ray machines are used for the examination of dental tissue. Also apparatuses for measuring dense tissue by means of ultrasound are known in the art. The publication (Development and Application of an Ultrasonic Imaging System for Dental Diagnosis. H. Fukukita, T. Yanco, A. Fukumoto, K. Sawada, T. Fujimasa, and I. Sciaenidae. Journal Of Clinical Ultrasound No. 13, 597-600, October 1985), describes an ultrasound measurement method for examining teeth.
Because of the health hazards caused by high power levels required for x-ray fluoroscopy, it is impossible to obtain real-time information. More importantly the power level of X-rays used in dental offices cannot penetrate metal crowns used in tooth restoration. This means secondary caries and cracks in the tooth under the crown cannot be diagnosed.
In stress (acoustic) waves ultrasonic and sonic refer only to the frequency of excitation, ultrasonic being frequencies above 20 KHz used to impart a wave into the material. The velocity of a stress wave is dependent on the material properties only, not the frequency of excitation. All commercially available timing units give comparable results if calibrated and operated according to the manufacturers direction.
In existing art of ultrasonic procedure, an electrical device known as a pulser/receiver generates an electrical pulse to a transducer that changes the electrical pulse into an ultrasonic pulse (stress wave). The transducer, in turn, directs the ultrasonic pulse to any desired surface where it is transmitted thru that object and out the other side. The ultrasonic pulse received by a second transducer, the receiving transducer, is converted by said transducer to an electrical pulse for display on the cathode ray tube of the oscilloscope or other data processing equipment.
Ultrasonic devices such as transducers can be coupled to an object by air or water. While water is effective it is hard to use in an open environment such as a mouth. Transducers are more effective when used with a coupling medium such as acoustical gel or ultrasonic coupling devices. An ultrasonic coupling device could be a bladder made of an ultrasonic conducting membrane and filled with an ultrasonic conducting material like silicon, water, oil, etc. Focused ultrasonic transducers in prior art refer to transducer designed to concentrate ultrasonic sound waves to a spot at the focal length of the given transducer. This spot is usually much smaller in diameter than the face of the transducer. This focusing effect is the same for transmitting and receiving. By focusing a given transducer there is an increase in gain in the ultrasonic signal and an increase in the resolution of the device often to parts of a millimeter.
We propose the use of two classes of arrays of stress (acoustic) transducers. The first class represents one-dimensional arrays where the transducers are arranged in either a straight line (a linear array) on a curved line (curvilinear array). The second class represents two-dimensional arrays where the transducers are arranged on either a flat rectilinear grid or on a curved grid.
A phased array is an array of transducers and electronic circuitry that produce a focused receive and/or transmit stress (acoustic) beam. It functions in a manner similar to phased array RADAR.
It is an object of the invention to provide a method of detecting dental lesions under a gold crown or other dental restoration.
It is further an object of the invention to provide a method of detecting dental lesions under the gum line.
It is further an object of the invention to provide a method of detecting dental lesions in the interproximal area.
It is further an object of the invention to provide a non-invasive method of detecting or diagnosing periodontal disease.
It is also an object of the invention to be able to provide real-time ultrasonic tomography, a form of mapping or imaging, of a tooth and surrounding gum and bone material.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.